The present invention relates to a hybrid silicon wafer comprising the functions of both a polysilicon wafer and a single-crystal wafer, and to the method for manufacturing such a hybrid silicon wafer.
In the silicon semiconductor manufacturing process, a wafer prepared based on single-crystal growth is primarily used. This single-crystal silicon wafer has increased in size with the times, and it is anticipated to be of φ 400 mm or larger in the near future. In addition, a so-called mechanical wafer for testing is now required in order to establish the apparatus and peripheral technology necessary for the semiconductor manufacturing process.
Generally speaking, since this kind of mechanical wafer is subject to fairly high precision testing, it needs to possess characteristics similar to the mechanical properties of a single-crystal silicon. Thus, if used for testing, the actual single-crystal silicon wafer was conventionally being used as is. However, since a single-crystal silicon wafer of φ 400 mm or larger is extremely expensive, an inexpensive wafer having similar characteristics to single-crystal silicon is in demand.
Meanwhile, as a component of such semiconductor manufacturing equipment, a proposal has also been made for using a sputtering target made out of a rectangular or disk-shaped silicon plate. While the sputtering method is being used as a means for forming thin films, there are several sputtering methods including the bipolar DC sputtering method, frequency sputtering method, magnetron sputtering method and the like, and thin films of various electronic parts are being formed using the sputtering characteristics unique to the respective methods.
This sputtering method is to place a substrate as the anode opposite to a target as the cathode, and generate an electrical field by applying a high voltage between the foregoing substrate and target under an inert gas atmosphere; and is based on the principle that ionized electrons and inert gas collide to form a plasma, the cations in the plasma collide with the target surface to knock out the target constituent atoms, and the discharged atoms adhere to the opposite substrate surface so as to form a film.
A sintered polysilicon is proposed for this kind of sputtering target, and this sintered compact target is required to be of considerable thickness and in a large rectangle or discoid shape in order to improve the deposition efficiency. Moreover, a proposal has also been made for using this sintered polysilicon as a board for retaining the single-crystal silicon wafer. Nevertheless, a polysilicon entails significant problems in that the sinterability is inferior, and the obtained products have low density and the low mechanical strength.
In light of the above, in order to improve the characteristics of the foregoing sintered silicon target, proposed is a sintered silicon formed by performing compression molding and sintering to the silicon powder obtained by being heated under reduced pressure and within a temperature range of 1200° C. or higher but less than the melting point of silicon to deoxidize, and setting the crystal grain size of the sintered compact to be 100 μm or less (for instance, refer to Patent Document 1).
However, if the thickness of the target manufactured as described above is thin; for instance, 5 mm or less, the density will relatively increase and the strength will also increase. But if the thickness becomes any thicker, the density will continue to be low (less than 99%), and the mechanical strength will also deteriorate. Thus, there is a problem in that it is not possible to manufacture a large-size rectangular or disk-shaped target.
In light of the foregoing circumstances, the present applicant previously proposed a sintered silicon in which the average crystal grain size is 50 μm or less and the relative density is 99% or more, and its production method (refer to Patent Document 2).
Although this sintered silicon possesses numerous advantages including high density and high mechanical strength, the further improvement of these characteristics is being demanded, and the applicant filed a patent application relating to technology that improved the foregoing points.
Since a wafer using the foregoing sintered silicon has similar mechanical properties as a single-crystal silicon, it can be used as a dummy wafer for the transport system of semiconductor manufacturing equipment or the development of robotics. In addition, the application as a base substrate of an SOI wafer is also being considered.
Nevertheless, these are all polysilicons made from a sintered silicon. Although there are numerous points that are similar to the physical properties of a single crystal, they do not possess the function as the single crystal itself, and there is a fundamental problem in that they cannot be used for process testing such as deposition experiments.    [Patent Document 1] Japanese Patent No. 3342898    [Patent Document 2] Japanese Patent No. 3819863